Memory apparatus and system with shared wordline decoder

ABSTRACT

A memory device includes wordline decoder circuits that share components between adjacent memory blocks. The wordline decoder circuits include multiple levels, where at least one level is split, driving half of the wordlines in one adjacent memory block and driving half of the wordlines in another adjacent memory block. Memory blocks have every other wordline coupled to one adjacent decoder circuit, and the remaining wordlines coupled to another adjacent decoder circuit.

FIELD

The present invention relates generally to memory devices, and morespecifically to wordline decoding in memory devices.

BACKGROUND

Semiconductor memory devices continue to shrink in size. Semiconductordevices in general continue to shrink because device minimum featuresizes continue to shrink. Reduced feature sizes result in higher memorystorage density per unit die area and reduce die cost. Memory storagedensity per unit die area can also be increased by increasing theefficiency with which the memory array and related circuits areorganized on the die.

Outside of the memory array, decoder circuits consume the largestsilicon area of repeated structures on large density die (>128 Mb).Reducing the area of the decoders will significantly increase storagedensity per unit die area and reduce the cost of the die.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention are illustrated by way of example and notlimitation in the figures of the accompanying drawings, in which:

FIG. 1 shows an electronic system in accordance with various embodimentsof the invention;

FIG. 2 show a memory device in accordance with various embodiments ofthe invention;

FIG. 3 shows wordline pre-decoders in accordance with variousembodiments of the present invention;

FIG. 4 shows one wordline selection path in a shared wordline decoder inaccordance with various embodiments of the invention;

FIG. 5 shows a memory array in accordance with various embodiments ofthe invention;

FIG. 6 shows a memory block with shared wordline decoders in accordancewith various embodiments of the invention;

FIG. 7 shows memory blocks and shared wordline decoders in a partitionof a memory device in accordance with various embodiments of theinvention;

FIG. 8 shows a shared wordline decoder structure in accordance withvarious embodiments of the invention; and

FIG. 9 shows a flow diagram in accordance with various embodiments ofthe present invention.

DESCRIPTION OF EMBODIMENTS

In the following detailed description, reference is made to theaccompanying drawings that show, by way of illustration, specificembodiments in which the invention may be practiced. These embodimentsare described in sufficient detail to enable those skilled in the art topractice the invention. It is to be understood that the variousembodiments of the invention, although different, are not necessarilymutually exclusive. For example, a particular feature, structure, orcharacteristic described herein in connection with one embodiment may beimplemented within other embodiments without departing from the scope ofthe invention. In addition, it is to be understood that the location orarrangement of individual elements within each disclosed embodiment maybe modified without departing from the scope of the invention. Thefollowing detailed description is, therefore, not to be taken in alimiting sense, and the scope of the present invention is defined onlyby the appended claims, appropriately interpreted, along with the fullrange of equivalents to which the claims are entitled. In the drawings,like numerals refer to the same or similar functionality throughout theseveral views.

Use of the terms “coupled” and “connected”, along with theirderivatives, may be used. It should be understood that these terms arenot intended as synonyms for each other. Rather, in particularembodiments, “connected” may be used to indicate that two or moreelements are in direct physical or electrical contact with each other.“Coupled” my be used to indicate that two or more elements are in eitherdirect or indirect (with other intervening elements between them)physical or electrical contact with each other, and/or that the two ormore elements co-operate or interact with each other (e.g. as in a causean effect relationship).

FIG. 1 shows a system 100 in accordance with various embodiments of thepresent invention. System 100 may be any type of device that includesmemory without departing from the scope of the present invention. Forexample, system 100 may be a computer or a mobile phone with nonvolatilememory. Also for example, system 100 may be a global positioning system(GPS) receiver or a portable media player with nonvolatile memory.

The wireless architecture embodiment illustrated in FIG. 1 shows acommunications device 100 that includes one or more memory devices withshared wordline decoder circuits in accordance with the presentinvention. It should be noted that the present invention is not limitedto wireless communication embodiments and other, non-wirelessapplications may use the present invention. As shown in this wirelessembodiment, communications device 100 includes one or more antennastructures 114 to allow radios to communicate with other over-the-aircommunication devices. As such, communications device 100 may operate asa cellular device or a device that operates in wireless networks suchas, for example, Wireless Fidelity (Wi-Fi) that provides the underlyingtechnology of Wireless Local Area Network (WLAN) based on the IEEE802.11 specifications, WiMax and Mobile WiMax based on IEEE 802.16-2005,Wideband Code Division Multiple Access (WCDMA), and Global System forMobile Communications (GSM) networks, although the present invention isnot limited to operate in only these networks. The radio subsystemscollocated in the same platform of communications device 100 provide thecapability of communicating with different frequency bands in anRF/location space with other devices in a network. It should beunderstood that the scope of the present invention is not limited by thetypes of, the number of, or the frequency of the communication protocolsthat may be used by communications device 100.

The embodiment illustrates the coupling of antenna structure 114 to atransceiver 112 to accommodate modulation/demodulation. In general,analog front end transceiver 112 may be a stand-alone Radio Frequency(RF) discrete or integrated analog circuit, or transceiver 112 may beembedded with a processor having one or more processor cores. Themultiple cores allow processing workloads to be shared across the coresand handle baseband functions and application functions.

Processor 110 includes at least first core 116; in the embodimentdepicted in FIG. 1 processor 110 also includes second core 118, and eachcore may include memory. For example, first core 116 may includevolatile or nonvolatile memory such as phase change memory (PCM), FLASH,or RAM. Each core may include any combination of different types ofmemory without departing from the scope of the present invention.Processor 110 may execute instructions from any suitable memory withinsystem 100. For example, any memory within a processor core, or any ofthe memory devices within system memory 120, may be considered acomputer-readable medium that has instructions stored that when accessedcause processor 110 to perform according to embodiments of theinvention.

First core 116 and second core 118 may also make use of Magnetic RandomAccess Memory (MRAM), which employs magnetic storage elements formedfrom two ferromagnetic plates located at an intersection of a row andcolumn line and selected by a Magnetic Tunnel Junction (MTJ) device.Current imparted to the row line in one direction causes a magneticfield operative on the MRAM cell biasing the MRAM cell toward a binarystate. Due to a magnetic tunnel effect, the electrical resistance of thememory cell changes based on the orientation of the fields in the twoplates.

First core 116 and the second core 118 may also make use ofFerro-electric Random Access Memory (FRAM), which employs memory cellsthat may include one transistor and one capacitor. The capacitorincludes ferroelectric material and a bi-stable atom in theferroelectric material that is shifted to form two stable polarizationstates. Memory cell data may be written by positively or negativelyorienting the dipoles of the ferroelectric material via an appliedpolarizing voltage. Data may be read by detecting the voltage of the bitline (BL) connected with the memory cell. Current feed circuits supplyelectric currents to the bit lines for a predetermined period from astart of a read operation, and read control circuitry senses thedirection of the electric polarization as either a high or a low logicstate. Each orientation is stable and remains in place even after theelectric field is removed, preserving the data within the memory withoutperiodic refresh.

Processor 110 is shown including a host controller with a memoryinterface to system memory 120. While the host controller is shown withonly an interface to system memory 120, this is not a limitation of thepresent invention. For example, processor 110 may communicate withmemory devices in system memory 120, a solid state disk (SSD) withmemory (not shown), a magnetic storage disk (not shown) or any othertype of device.

System memory 120 may be provided by one or more different types ofmemory having shared wordline decoder circuits. The memories withinsystem memory 120 may be combined in a stacking process to reduce thefootprint on a board, packaged separately, or placed in a multi-chippackage with the memory component placed on top of the processor. Theembodiment also illustrates that one or more of the processor cores maybe embedded with nonvolatile memory 132 having shared wordline decodercircuits.

System memory 120 includes FLASH memory 122, phase change memory (PCM)124, and other memory 126. FLASH memory 124 stores information bystoring charge on a floating gate in a Metal Oxide Semiconductor (MOS)transistor. The stored charge alters the threshold voltage of thetransistor, and the difference in threshold voltage is “read” todetermine whether the stored information is a “0” or a “1”. In someembodiments, varying amounts of charge are stored on the floating gateto represent more than one bit of information per memory cell. This issometimes referred to as Multi-Level Cell (MLC) FLASH. FLASH memory 124may be any type of FLASH memory, including NOR FLASH memory, NAND singlelevel cell (SLC) memory, or NAND multi-level cell (MLC) memory.

System memory 120 also includes phase change memory (PCM) 122. PCM ismemory that stores information based on modifiable material properties,such as whether a material is in a crystalline or an amorphous state(phase). For example, in some embodiments, phase change memories includealloys of elements of group VI of the periodic table, such as Te or Se,that are referred to as chalcogenides or chalcogenic materials.Chalcogenides may be used advantageously in phase change memory cells toprovide data retention and remain stable even after the power is removedfrom the nonvolatile memory. Taking the phase change material asGe₂Sb₂Te₅ for example, two phases or more are exhibited having distinctelectrical characteristics useful for memory storage. Phase changememory may be referred to as a Phase Change Memory (PCM), Phase-ChangeRandom Access Memory (PRAM or PCRAM), Ovonic Unified Memory (OUM),Chalcogenide Random Access Memory (C-RAM), or by other suitable names.

Memory devices within system memory 120 may be packaged in any manner.For example, in some embodiments, FLASH memory 122, PCM 124, and othermemory 126 may be combined in a stacking process to reduce the footprinton a board, packaged separately, or placed in a multi-chip package withthe memory component placed on top of the processor. The FLASH memory122 may comprise multiple FLASH memories to increase capacity and/orbandwidth.

FIG. 2 show a memory device in accordance with various embodiments ofthe invention. Memory device 200 includes memory array 230, sharedwordline (WL) decoders 220, and pre-decoders 210. Memory device 200 maybe any type of memory device (e.g., FLASH, RAM, PCM, MRAM, FRAM, etc.)and may be utilized anywhere in a system (e.g., memory embedded in aprocessing core, system memory, solid state disk, etc.).

Memory device 200 is illustrated with a minimum of components toaccentuate the decoding of address lines to wordlines. In practice,memory device 200 includes many other structures not shown in FIG. 2.For example, memory device 200 may include sense amplifiers, voltagereferences, programming circuits, charge pumps, logic circuits, pads,any many other structures.

Pre-decoders 210 receive address lines A[10:0] and provide partiallydecoded output signals L1X[31:0], L2X[7:0], and L3X[7:0]. The example ofFIG. 2 shows eleven address lines, but this is not a limitation of thepresent invention. Any number of address lines (corresponding to anyarray density) may be present. FIG. 3 shows an example pre-decodingstructure to decode A[10:0] into L1X[31:0], L2X[7:0], and L3X[7:0].L1X[31:0] are referred to as the “level one x-decode signals;” L2X[7:0]are referred to as the “level two x-decode signals;” and L3X[7:0] arereferred to as the “level three x-decode signals.”

The various levels of decode signals (L1X, L2X, L3X) drive differentportions of the shared wordline decoders 220. For example, L1X drive“level one decoders,” L2X drive “level two decoders,” and L3X drive“level three decoders.” The various levels of wordline decoders aredistributed about memory array 230, and at least one level is sharedamong adjacent memory blocks. Although three levels of pre-decoding areshown in FIGS. 2 and 3, this is not a limitation of the presentinvention. For example, in some embodiments, there may be a fourthlevel, a fifth level, etc.

FIG. 4 shows one wordline selection path in a shared wordline decoder inaccordance with various embodiments of the invention. Circuit 400includes selection transistors 410, 420, and 430. As shown in FIG. 4,any one wordline is selected when all of the selection transistors inthe corresponding selection path are conducting. The selectiontransistors are conducting when the corresponding level one, two, andthree decoder signals are asserted.

Selection transistor 410 is one transistor in a level one decoder,selection transistor 420 is one transistor in a level two decoder, andselection transistor 430 is one transistor in a level three decoder.When all three selection transistors are on, the wordline is selected.In some embodiments, the level one decoder is a split decoder thatdrives wordlines in more than one memory block. For example, half of theselection transistor in the level one decoder may drive wordlines in oneadjacent memory block, while the other half of the selection transistorsin the level one decoder may drive wordlines in another adjacent memoryblock. This is described in more detail below.

In some embodiments, the level two and level three decoders are “shared”between adjacent memory blocks. For example, selection transistors inthe level one decoder, although driving wordlines in adjacent memoryblocks, are selected in common by transistors in the level two and threedecoders. This is also described in more detail below. In someembodiments, more than three levels of wordline decoders are provided,and/or more than two levels are shared. For example, additionalpre-decoders may provide L4X, L5X, or more decode signals. In theseembodiments, additional selection transistors are included in eachwordline selection path.

FIG. 5 shows a memory array in accordance with various embodiments ofthe invention. Memory array 500 includes memory blocks 520 interspersedwith shared wordline decoders 530. Memory array 500 includes repeatingstructures, referred to herein as “tiles.” In the example of FIG. 5, thearray includes 16×16 tiles. One row of tiles is referred to as apartition. One example partition 510 is called out in FIG. 5.Pre-decoders (not shown) decode address lines and drive the sharedwordline decoders 530 with L1X, L2X, and L3X signals. Within a givenpartition, shared wordline decoders 530 that are adjacent to multiplememory blocks drive wordlines in the multiple adjacent memory blocks.

FIG. 6 shows a memory block with shared wordline decoders in accordancewith various embodiments of the invention. Memory block 630 correspondsto one of memory blocks 520 in memory array 500, and shared wordlinedecoders 610 and 620 correspond to shared wordline decoders 530 oneither side of the memory block. Level one decoders within sharedwordline decoders 610 and 620 are split, each driving half of thewordlines in memory block 630. Level two and level three decoders withinshared wordline decoders 610 and 620 are shared.

In some embodiments, every other wordline in a memory block is driven bya shared wordline decoder adjacent to the memory block on side, and theremaining wordlines are driven by a shared wordline decoder adjacent tothe memory block on another side. For example, shared wordline decoder610 drives even numbered wordlines 614 in memory block 630, and sharedwordline decoder 620 drives odd numbered wordlines 622 in memory block630. Driving every other wordline in a memory block allows the level onedecoder to match the pitch of every other wordline in the memory block.

FIG. 7 shows memory blocks and shared wordline decoders in a partitionof a memory device in accordance with various embodiments of theinvention. Partition 510 of FIG. 7 corresponds to partition 510 of FIG.5 with 16 memory blocks. Shared wordline decoders are positioned betweenadjacent memory blocks. As an example, shared wordline decoder 610 is amulti-level wordline decoder that includes a level one decoderrepresented by transistors 710 and 712; a level two decoder representedby transistor 720, and a level three decoder represented by transistor730. The level one decoder is split into two sections: the first sectionto drive half of the wordlines 612 in the memory block to the left; anda second section to drive half of the wordlines 614 in the memory blockto the right. The level two decoder and the level three decoder areshared between the memory blocks to the left and right.

The level one decoding is unique to each memory block and as shown inFIG. 7, each memory block has level one decoders along two oppositesides of the block. The level one decoder on one side of the memoryblock is coupled to all of the even wordlines in the block and the levelone decoder on the other side of the memory block is coupled to all ofthe odd wordlines in the block.

Level two and level three decoders outside the outer most blocks onlydrive wordlines in a single block, and so the level two and level threedecoders in these decoders are not shared across multiple memory blocks.For example, decoder 710 only drives wordlines in memory block 0, anddecoder 720 only drives wordlines in memory block 15.

FIG. 8 shows a shared wordline decoder structure in accordance withvarious embodiments of the invention. As shown in FIG. 8, eightselection transistors exist in the level three (L3X level). Gates of theL3X selection transistors are driven by L3X[7:0]. For each of the eightL3X selection transistors, there exists eight L2X transistors. Gates ofthe L2X transistors are driven by L2X[7:0]. For each of the L2Xselection transistors, there exists 32 L1X transistors. Gates of the L1Xtransistors are driven by L1X[31:0].

During wordline selection, the assertion of one signal in L3X[7:0] turnson one L3X selection transistor, which selects one group of eight L2Xselection transistors. The assertion of one signal in L2X [7:0] in turnselects one group of 32 L1X selection transistors. Up to this point, thedecoding is shared between two adjacent memory blocks. The assertion ofone signal in L1X[31:0] will provide the final selection of a wordline.The selected wordline will either be an odd wordline coupled to a memoryblock on one side, or an even wordline coupled to a memory block on theother side. Accordingly, the level one decoders are split, and the leveltwo and level three decoders are shared.

FIG. 9 shows a flow diagram in accordance with various embodiments ofthe present invention. At 910, a first subset of address lines in amemory device are decoded. This corresponds to the operation of apre-decoder such as those shown in FIGS. 2 and 3. Specifically, this maycorrespond to the decoding of A[4:0] to L1X[31:0]. Also at 910, a splitfirst level decoder is driven to select wordlines in one of two memoryblocks. This corresponds to one signal in L1X[31:0] selecting awordline. The first level decoder is split to drive half of thewordlines in one adjacent memory block and to drive one half of thewordlines in another adjacent memory block. For example, if an evenwordline is selected, then a wordline in a memory block to the rightwill be selected, and if an odd wordline is selected, then a wordline ina memory block to the left will be selected.

At 920, a second subset of address lines in the memory device isdecoded, and a second decoder is driven to enable the split leveldecoder. This corresponds to the operation of either or both of thepre-decoders that decode A[7:5] and A[10:8], and driving either or bothof the level two and level three decoders with L2X[7:0] and L3X[7:0],respectively.

Although the present invention has been described in conjunction withcertain embodiments, it is to be understood that modifications andvariations may be resorted to without departing from the scope of theinvention as those skilled in the art readily understand. Suchmodifications and variations are considered to be within the scope ofthe invention and the appended claims.

1. A memory device comprising: two memory blocks, each includingwordlines; and a decoder circuit positioned between the two memoryblocks, the decoder circuit being coupled to one half of the wordlinesin a first of the two memory blocks and to one half of the wordlines inthe second of the two memory blocks.
 2. The memory device of claim 1wherein the decoder circuit is coupled to every other wordline in thefirst of the two memory blocks and to every other wordline in the secondof the two memory blocks.
 3. The memory device of claim 1 wherein thedecoder circuit comprises: a split first level coupled to the wordlinesin the two memory blocks; and a shared second level coupled to the splitfirst level.
 4. The memory device of claim 3 wherein the decoder circuitfurther comprises a shared third level coupled to the shared secondlevel.
 5. The memory device of claim 3 further comprising a firstpre-decoder circuit coupled to pre-decode a first subset of addresslines and to drive the split first level of the decoder circuit.
 6. Thememory device of claim 5 further comprising a second pre-decoder circuitcoupled to pre-decode a second subset of address lines and to drive theshared second level of the decoder circuit.
 7. The memory device ofclaim 6 further comprising: a shared third level within the decodercircuit coupled to the shared second level; and a third pre-decodercircuit coupled to pre-decode a third subset of address lines and todrive the shared third level of the decoder circuit.
 8. A memory devicecomprising: a plurality of memory blocks; and a plurality of multi-levelshared wordline decoders, each of the plurality of multi-level sharedwordline decoders including a split first level and a shared secondlevel, the split first level being split into two sections, the twosections including selection transistors coupled to wordlines indifferent ones of the plurality of memory blocks, and the shared secondlevel being coupled in common to the two sections of the split firstlevel.
 9. The memory device of claim 8 wherein the plurality of memoryblocks are arranged in rows, and each of the plurality of multi-levelshared wordline decoders is positioned between memory blocks in a row.10. The memory device of claim 9 wherein each of the plurality ofmulti-level shared wordline decoders is coupled to wordlines in adjacentmemory blocks.
 11. The memory device of claim 10 wherein each of theplurality of memory blocks has even wordlines coupled to one multi-levelshared wordline decoder on a first side and odd wordlines coupled toanother multi-level shared wordline decoder on a second side.
 12. Thememory device of claim 8 further comprising a plurality of pre-decodersto separately enable the split first level and shared second level ofthe multi-level shared wordline decoders.
 13. An electronic systemcomprising: a wireless interface; a processor coupled to the wirelessinterface; and a memory device having at least two memory blocks, eachincluding wordlines, and a decoder circuit positioned between the twomemory blocks, the decoder circuit being coupled to one half of thewordlines in a first of the two memory blocks and to one half of thewordlines in the second of the two memory blocks.
 14. The electronicsystem of claim 13 wherein the decoder circuit is coupled to every otherwordline in a first of the two memory blocks and to every other wordlinein a second of the two memory blocks.
 15. The electronic system of claim13 wherein the decoder circuit comprises: a split first level coupled tothe wordlines in the two memory blocks; and a shared second levelcoupled to the split first level.
 16. The electronic system of claim 15wherein the decoder circuit further comprises a shared third levelcoupled to the shared second level.
 17. The electronic system of claim15 further comprising a plurality of pre-decoders to separately enablethe split first level and shared second level of the decoder circuit.18. A method comprising: partially decoding a first subset of addresslines in a memory device and driving a split first level decoder thatselects wordlines in one of two memory blocks; and partially decoding asecond subset of address lines in the memory device and driving a seconddecoder that enables the split first level decoder.
 19. The method ofclaim 18 wherein driving a split first level decoder that selectswordlines in one of two memory blocks comprises driving a split firstlevel decoder that is coupled to every other wordline in a first memoryblock and every other wordline in a second memory block.
 20. The methodof claim 18 further comprising partially decoding a third subset ofaddress lines in the memory device and driving a third decoder thatenables the second decoder.